Method and apparatus for blind transport format detection using discontinuous transmission (DTX) detection

ABSTRACT

Methods and apparatus are provided for blind transport format detection using Discontinuous Transmission (DTX) detection. According to one aspect of the invention, the transport format that was used to transmit information is determined by identifying a transition between a Discontinuous Transmission segment and a data segment included in the transmitted information; and determining the transport format based on a location of the transition of the Discontinuous Transmission segment. A cyclic redundancy check can optionally be performed for a plurality of possible transport formats, and then the step of identifying a transition can be limited to those transport formats having a valid cyclic redundancy check.

FIELD OF THE INVENTION

The present invention is related to communication techniques and, moreparticularly, to techniques for detecting a transport format in acommunication system.

BACKGROUND OF THE INVENTION

A communication network transfers information, such as voice, video andtelemetry, among the User Equipment (UE) of subscribers. Information,such as broadband Internet data, broadcast services, and network controldata, can be transferred between the network itself and the subscriberUEs. A number of existing networks, such as Wideband Code DivisionMultiple Access (WCDMA), Code Division Multiple Access (3rd Generationcellular/radio technology) (CDMA2000), and Worldwide Interoperabilityfor Microwave Access, Inc. (WiMAX), according to the IEEE 802.16wireless broadband standard, support parallel operation of a pluralityof such information services. For such support, and for optimization ofthe network capacity, these networks must be able to transferinformation at rapidly changing data rates. The networks must also beable to combine the different services into a single physical datastream, used to transfer the combined information over the physicalchannel.

The Transport Layer typically combines data of different rates. Thecombination of information services and data rates changes rapidly.Thus, the transmitter must notify the receiver of the change at highrates. Most systems attach an additional header to transmitted data,describing the service combination format and data rates of thecurrently transferred data. This addition, naturally, increases theoverhead.

In WCDMA (UMTS), for example, each service is related to a transportchannel (TrCH). The service combination and data rate selection formatused to combine the TrCHs into a physical data stream coded compositetransport channel (CCTrCH), is referred to as a transport formatcombination (TFC). A transport format combination indicator (TFCI) isattached to each frame of data to indicate which the TFC that wasselected. The receiver uses the TFCI to select the format for thedecoding and separation of data into the different services. Thisprocess is referred to as TFCI signaling.

A number of techniques have been proposed or suggested for conservingthe bandwidth required for TFCI signaling. For example, a BlindTransport Format Detection (BTFD) method was introduced in “Multiplexingand Channel Coding (FDD),” 3rd Generation Partnership Project, TechnicalSpecification Group Radio Access Network, 3GPP TS 25.212 V4.5.0(2002-06). The disclosed Blind Transport Format Detection method detectsthe TFC with a blind algorithm.

A Blind Transport Format Detection method must perform three types ofTrCHs detection, namely, single, explicit, and guided transport channelformat detection. A single transport format detected TrCH has atransport set not containing more than one transport format with morethan zero transport blocks and that does not use guided detection. Thetransport format with more than zero transport blocks must have CRC withnon-zero length. Energy detection and a cyclic redundancy check (CRC)are used to blindly detect the transport format transmitted by thesingle transport format detected TrCH when this TrCH is the only TrCH ofthe CCTrCH.

Explicit and guided transport format detected TrCHs are non-signaledTrCHs that have more than one transport format and do not use singledetection. An explicitly detected TrCH must have at least one blocktransmitted every Transmission Time Interval (TTI). Each block of anexplicitly detected TrCH is appended with a non-zero CRC. Guideddetection is used on a TrCH with zero length CRC that is associated withan explicitly detected TrCH. By detecting the transport format of anexplicitly detected TrCH, the transport format of the associated guideddetected TrCH is also decided.

In order to perform explicit and single detections, CRC is checked forall possible transport format combinations. A valid TFC (transportformat combination) is selected if the CRC was valid for all TrCHs inthe CCTrCH using this combination. This technique, however, canintroduce a misdetection of the TFC, since statistically, CRC checks ofall TrCHs may be erroneously valid for a TFC that was not transmitted. Aneed therefore exists for a Blind Transport Format Detection method thatavoids the misdetection problem.

SUMMARY OF THE INVENTION

Generally, methods and apparatus are provided for blind transport formatdetection using Discontinuous Transmission detection. According to oneaspect of the invention, the transport format that was used to transmitinformation is determined by identifying a transition between aDiscontinuous Transmission segment and a data segment included in thetransmitted information; and determining the transport format based on alocation of the transition of the Discontinuous Transmission segment.

For example, a size of the Discontinuous Transmission segment can beidentified and the transport format can be determined based on the size.In a further variation, an energy associated with the data segmentrelative to energy of a reference segment is determined, and thetransport format can be determined based on the energy associated withthe data segment.

A cyclic redundancy check can optionally be performed for a plurality ofpossible transport formats, and then the step of identifying atransition can be limited to those transport formats having a validcyclic redundancy check. For example, a start of DTX address can bedetermined for each of the transport formats having a valid cyclicredundancy check.

A more complete understanding of the present invention, as well asfurther features and advantages of the present invention, will beobtained by reference to the following detailed description anddrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an exemplary memory segmentation of a firstdeinterleaver;

FIG. 2 illustrates pseudo code for an exemplary blind transport formatdetection process incorporating features of the present invention; and

FIG. 3 illustrates the execution of the exemplary blind transport formatdetection process of FIG. 2 for a memory segment where there are threetransport formats with valid CRCs.

DETAILED DESCRIPTION

The present invention provides a Blind Transport Format Detection methodand apparatus that avoid the misdetection of the TFC by using aDiscontinuous Transmission (DTX) detection technique. As used herein,the term “Discontinuous Transmission” or “DTX” shall apply to anytemporary situation where the transmitting side transmits at a reducedpower level, relative to the transmission of data or payload, for aspecific user. Typically, the transmitting side does not transmit anypower for a specific user when transmitting the DTX. While there may bedifferent reasons in different systems or under different scenarios touse DTX (e.g., saving power, introducing less interference to otherusers and reducing the number of transmitted bits), the DTX allows thepresent invention to determine the transport format, as would beapparent to a person of ordinary skill in the art.

Blind Transport Format Detection Using Path-Metric Values at SurvivingPaths

In order to prevent the misdetection of a TFC, an additional operationis required to test the validity of the detection of each of the TrCHsin the CCTrCH. The above-cited 3GPP TS 25.212 V4.5.0 specificationsuggests using the path-metric values at the surviving paths of theViterbi decoding of each of the TrCHs. The path-metric value of the zerostate and the minimum and maximum values of the remaining states areused to calculate the scatter of the Viterbi decoding in the followingmanner:

${S({\mathbb{i}})} = {{- 10}{{\log\left( \frac{{a_{0}({\mathbb{i}})} - {a_{\min}({\mathbb{i}})}}{{a_{\max}({\mathbb{i}})} - {a_{\min}({\mathbb{i}})}} \right)}\lbrack{dB}\rbrack}}$where i is the TFI of detected TrCH; S(i) is the scatter of Viterbidecoding; a₀(i) is the zero path-metric value; a_(min)(i) is the minimumof remaining path-metric values; and a_(max)(i) is the maximum ofremaining path-metric values.

The detection of a transport format is considered valid if the value ofS(i) is greater than a predefined threshold, D. Generally, the transportformat with the largest scatter is selected from all the TrCHs that passthe CRC check, and are considered valid according to the above method.

This method is applicable as long as access to the path-metric of theViterbi decoder is available. This, however, is not necessarilyguaranteed when integrating a 3G chip, composed of various cores andcoprocessors. Also, addition of path-metric access in a Viterbi decoderdesign, naturally, requires an increase in silicon volume. In addition,this method does not supply a complete solution to the single transportformat detected TrCH, in which a zero block transport format is presentand does not go through the Viterbi decoding stage.

Blind Transport Format Detection Using DTX Detection

The present invention provides a Blind Transport Format Detection methodand apparatus that avoid the misdetection of the TFC by using a DTXdetection technique. The present invention provides a method forpreventing the misdetection of a TFC by attaining energy relatedinformation from an accessible memory component, allowing easyprocessing of the stored data. In one exemplary implementation,misdetection of a TFC is achieved by attaining energy relatedinformation from the first deinterleaver. Since the first deinterleaveris a memory component, it can be accessed, allowing the stored data tobe processed. As discussed further below, the energy information allowsthe transition points from data to DTX to be identified, which allows aone-to-one mapping to the transport format.

FIG. 1 illustrates an exemplary memory segmentation of a firstdeinterleaver 100. The exemplary memory segmentation of the firstdeinterleaver 100 may be embodied, for example, as described in theabove-cited 3GPP TS 25.212 V4.5.0 specification. As shown in FIG. 1, thefirst deinterleaver stores a complete TTI of data for each TrCH in adesignated, predefined memory segment, such as segment 110-0. When themaximum size transport format is received for a TrCH, its wholedesignated memory segment 110 in the first deinterleaver 100 is filled(with no DTX). When, however, any other transport format is received,the memory segment is filled with data and DTX padding. The DTX paddingis stored at the end of each received frame of the TrCH in the memorysegment 110. There is always non-DTX data at the beginning of a frame,as the smallest transport format must have non-zero CRC.

The present invention recognizes that the size of the DTX segment has aone-to-one mapping to the Transport Format (a situation that is definedin the 3GPP specification as a Fixed Position mode). When usingcompressed mode by puncturing, such as shown in FIG. 1, p-bits replacethe first bits of the frame of the TrCH that is to be compressed. Theposition of amount of the p-bits in fixed position is similar for allpossible transport formats of the TrCH.

FIG. 2 illustrates pseudo code for an exemplary blind transport formatdetection process 200 incorporating features of the present invention.Generally, the blind transport format detection process 200 isimplemented when more than one possible transport format combination(TFC) has a valid CRC using the conventional method described above.Thus, the blind transport format detection process 200 shown in FIG. 2is used to distinguish between two or more transport formats, detectedwith a valid CRC for a single TrCH.

For each frame in a TTI of the processed TrCH, the blind transportformat detection process 200 initially attains the base address, A_(B),of the frame in the designated TrCH memory segment 110 during step 210.Thereafter, the blind transport format detection process 200 sorts all Ntransport formats with valid CRCs in descending order during step 220,such that the maximum size TF index equals 0 and the minimum size TFindex equals N−1.

For each transport format index, i, with a valid CRC, the blindtransport format detection process 200 then attains the start of the DTXaddress, A_(DTX)(i), during step 230. If p-bits present (forpuncturing), update the base address during step 240, as follows:A _(B) =A _(B)+number of p-bits.

The memory is divided into sub-segments during step 250, as follows:Seg(0)=A _(DTX)(1) . . . A _(DTX)(0). . .Seg(N−2)=A _(DTX)(N−1) . . . A _(DTX)(N−2)

A reference segment is defined during step 260:Seg(ref)=A _(B) . . . A _(DTX)(N−1)

The energy for reference segment is summed during step 270:

$E_{ref} = {\frac{1}{\text{length}\left( {{Seg}({ref})} \right)}{\sum\limits_{{Seg}{({ref})}}{soft\_ bit}^{2}}}$where p-bits are excluded from the integration if such bits appear inthe integration window. As discussed further below in conjunction withFIG. 3, the reference segment is known to be data, and E_(ref) providesa reference for the energy associated with data.

During step 280, the blind transport format detection process 200searches for non-DTX energy using a threshold, D, as follows:

for i=0 to N−2

$E = {\frac{1}{\text{length}\left( {{Seg}(i)} \right)}{\sum\limits_{{Seg}{(i)}}{soft\_ bit}^{2}}}$(excluding p-Bits, if present)

-   -   n=i    -   if E/E_(ref)<D, break    -   if n=N−2, n=n+1

end.

Thus, the energy is computed during step 280 for each segment. Asdiscussed further below in conjunction with FIG. 3, if E(0), forexample, is approximately equal to E_(ref), then segment 0 is data.Generally, this process identifies the DTX and data transitions. Aspreviously indicated, identifying the transition point from data to DTXprovides a one-to-one mapping to the transport format. The transportformat with index n is selected as the transport format during step 290.

If a single transport format detected TrCH is also present in theCCTrCH, its energy shall be calculated per frame over the whole memorysegment 110, scaled with the reference segment of the explicitlydetected TrCH, and compared to a threshold to decide whether data wastransmitted.

FIG. 3 illustrates the execution of the exemplary blind transport formatdetection process 200 for a memory segment 300 where there are three(N=3) transport formats with valid CRCs. Thus, the blind transportformat detection process 200 must determine which of the three potentialtransport formats with valid CRCs is the correct one. As shown in FIG.3, A_(DTX)(i), for i between 0 and 2, identifies the location of thestart of the DTX field for each of the 3 possible transport formats. Asindicated above, the reference segment, Seg(ref), helps to establish areference for the data energy. The reference segment near the baseaddress A_(B) of the frame is known to be data. The reference energy iscompared to the energy of each potential segment created by the start ofthe DTX field for each of the 3 possible transport formats. For example,for A_(DTX)(0), the portion of the memory segment 300 between the baseaddress A_(B) and A_(DTX)(0) (from right to left in FIG. 3), would bedata and the remaining portion would be DTX. If E(0) is approximatelyequal to E_(ref), then transport format i is selected.

While exemplary embodiments of the present invention have been describedwith respect to digital logic blocks, as would be apparent to oneskilled in the art, various functions may be implemented in the digitaldomain as processing steps in a software program, in hardware by circuitelements or state machines, or in combination of both software andhardware. Such software may be employed in, for example, a digitalsignal processor, micro-controller, or general-purpose computer. Suchhardware and software may be embodied within circuits implemented withinan integrated circuit.

Thus, the functions of the present invention can be embodied in the formof methods and apparatuses for practicing those methods. One or moreaspects of the present invention can be embodied in the form of programcode, for example, whether stored in a storage medium, loaded intoand/or executed by a machine, or transmitted over some transmissionmedium, wherein, when the program code is loaded into and executed by amachine, such as a computer, the machine becomes an apparatus forpracticing the invention. When implemented on a general-purposeprocessor, the program code segments combine with the processor toprovide a device that operates analogously to specific logic circuits.

It is to be understood that the embodiments and variations shown anddescribed herein are merely illustrative of the principles of thisinvention and that various modifications may be implemented by thoseskilled in the art without departing from the scope and spirit of theinvention.

We claim:
 1. A method for determining a transport format used totransmit information, comprising: identifying a location within adeinterleaver of a transition between a Discontinuous Transmissionsegment and a data segment included in said transmitted informationbased on energy related information derived from said deinterleaver; anddetermining said transport format by evaluating said identified locationof said transition of said Discontinuous Transmission segment.
 2. Themethod of claim 1, wherein said identifying step further comprises thestep of determining a size of said Discontinuous Transmission segment,and said determining said transport format step is based on said size.3. The method of claim 1, wherein said identifying step furthercomprises the step of determining an energy associated with said datasegment relative to energy of a reference segment, and said determiningstep is based on said energy associated with said data segment.
 4. Themethod of claim 1, wherein said transmitted information is a transmittedframe.
 5. The method of claim 1, further comprising the step ofevaluating a cyclic redundancy check for a plurality of possibletransport formats, and wherein said identifying step is only performedfor transport formats having a valid cyclic redundancy check.
 6. Themethod of claim 1, wherein said identifying step is performed fortransport formats having a valid cyclic redundancy check and wherein astart of DTX address is determined for each of said transport formatshaving a valid cyclic redundancy check.
 7. The method of claim 1,further comprising the step of updating a base address of saidinformation if puncturing is employed.
 8. A system for determining atransport format used to transmit information, comprising: a memory; andat least one processor, coupled to the memory, operative to: identify alocation within a deinterleaver of a transition between a DiscontinuousTransmission segment and a data segment included in said transmittedinformation based on energy related information derived from saiddeinterleaver; and determine said transport format by evaluating saididentified location of said transition of said DiscontinuousTransmission segment.
 9. The system of claim 8, wherein said processoris further configured to determine a size of said DiscontinuousTransmission segment, and said determining said transport format step isbased on said size.
 10. The system of claim 8, wherein said processor isfurther configured to determine an energy associated with said datasegment relative to energy of a reference segment, and saiddetermination is based on said energy associated with said data segment.11. The system of claim 8, wherein said transmitted information is atransmitted frame.
 12. The system of claim 8, wherein said processor isfurther configured to evaluate a cyclic redundancy check for a pluralityof possible transport formats, and wherein said identification is onlyperformed for transport formats having a valid cyclic redundancy check.13. The system of claim 8, wherein said identification is performed fortransport formats having a valid cyclic redundancy check and wherein astart of DTX address is determined for each of said transport formatshaving a valid cyclic redundancy check.
 14. The system of claim 8,wherein said processor is further configured to update a base address ofsaid information if puncturing is employed.
 15. A method for determininga transport format used to transmit information, comprising: evaluatinga cyclic redundancy check for a plurality of possible transport formats;identifying a location within a deinterleaver of a transition between aDiscontinuous Transmission segment and a data segment included in saidtransmitted information for transport formats having a valid cyclicredundancy check based on energy related information derived from saiddeinterleaver; and determining said transport format by evaluating saididentified location of said transition of said DiscontinuousTransmission segment.
 16. The method of claim 15, wherein saididentifying step further comprises the step of determining a size ofsaid Discontinuous Transmission segment, and said determining saidtransport format step is based on said size.
 17. The method of claim 15,wherein said identifying step further comprises the step of determiningan energy associated with said data segment relative to energy of areference segment, and said determining step is based on said energyassociated with said data segment.
 18. The method of claim 15, whereinsaid transmitted information is a transmitted frame.
 19. The method ofclaim 15, wherein a start of DTX address is determined for each of saidtransport formats having a valid cyclic redundancy check.
 20. The methodof claim 15, further comprising the step of updating a base address ofsaid information if puncturing is employed.